Servant Pascale, Le Coq Dominique, Aymerich Stéphane
Microbiologie et Génétique Moléculaire, INRA (UMR1238) and CNRS (UMR2585), Institut National Agronomique Paris-Grignon, F-78850 Thiverval-Grignon, France.
Mol Microbiol. 2005 Mar;55(5):1435-51. doi: 10.1111/j.1365-2958.2005.04473.x.
In Bacillus subtilis, the NADPH-dependent glyceraldehyde-3-phosphate dehydrogenase (GapB) and the phosphoenolpyruvate carboxykinase (PckA) enzymes are necessary for efficient gluconeogenesis from Krebs cycle intermediates. gapB and pckA transcription is repressed in the presence of glucose but not via CcpA, the major transcriptional regulator for catabolite repression in B. subtilis. A B. subtilis mini-Tn10 transposant library was screened for clones affected in catabolite repression of gapB. Inactivation of a previously unknown gene, yqzB (renamed ccpN for control catabolite protein of gluconeogenic genes), was found to relieve not only gapB but also pckA transcription from catabolite repression. Purified CcpN specifically bound to the gapB and pckA promoters. ccpN is co-transcribed constitutively with another unknown gene, yqfL. A yqfL deletion lowers the level of gapB and pckA transcription threefold under both glycolytic and gluconeogenic conditions and a ccpN deletion is epistatic over a yqfL deletion. YqfL is thus a positive regulator of the expression of gapB and pckA, the effect of which is not influenced by the metabolic regime of the cell but appears to be mediated by CcpN. ccpN has homologues in many Firmicutes, but not all, while yqfL homologues are widely distributed in Eubacteria and also present in some plants. In all analysed bacterial genomes, ccpN and yqfL are physically linked together or to putative gluconeogenic genes. CcpN thus orchestrates a novel CcpA-independent mechanism for catabolite repression of gluconeogenic genes highly conserved in Firmicutes and appears as a functional analogue of FruR in Enterobacteria. The physiological significance of the regulation mediated via the three B. subtilis global transcription regulators, CcpA, CggR and CcpN, is discussed.
在枯草芽孢杆菌中，NADPH 依赖性 3-磷酸甘油醛脱氢酶（GapB）和磷酸烯醇式丙酮酸羧激酶（PckA）对于从 Krebs 循环中间体高效进行糖异生是必需的。在葡萄糖存在的情况下，gapB 和 pckA 的转录受到抑制，但不是通过枯草芽孢杆菌中分解代谢物阻遏的主要转录调节因子 CcpA。对一个枯草芽孢杆菌 mini-Tn10 转座子文库进行筛选，以寻找在 gapB 的分解代谢物阻遏中受影响的克隆。发现一个先前未知的基因 yqzB（为糖异生基因的分解代谢物控制蛋白重新命名为 ccpN）失活不仅能解除 gapB 的分解代谢物阻遏，还能解除 pckA 的转录抑制。纯化的 CcpN 特异性结合到 gapB 和 pckA 启动子上。ccpN 与另一个未知基因 yqfL 组成型共转录。yqfL 的缺失在糖酵解和糖异生条件下均使 gapB 和 pckA 的转录水平降低三倍，并且 ccpN 的缺失相对于 yqfL 的缺失是上位性的。因此，YqfL 是 gapB 和 pckA 表达的正调节因子，其作用不受细胞代谢状态的影响，但似乎由 CcpN 介导。ccpN 在许多厚壁菌门细菌中存在同源物，但并非全部，而 yqfL 同源物广泛分布于真细菌中，并且在一些植物中也存在。在所有分析的细菌基因组中，ccpN 和 yqfL 在物理上彼此相连或与假定的糖异生基因相连。因此，CcpN 协调了一种独立于 CcpA 的新机制，用于厚壁菌门中高度保守的糖异生基因的分解代谢物阻遏，并且似乎是肠杆菌中 FruR 的功能类似物。讨论了通过枯草芽孢杆菌的三种全局转录调节因子 CcpA、CggR 和 CcpN 介导的调控的生理意义。
